fad-null: rename pcap_findalldevs() to pcap_findalldevs_interfaces()

This file is used on Debian GNU/Hurd where libpcap is expected to build,
even though it doesn't have the ability to do live captures.
Some changes didn't make it into 1.4.0.

Fix the CHANGES list by moving some changes that got in after the 1.4.0
release was made into a list for 1.4.1, and add some additional fixes to
that list.
snprintf() error to proper buffer

In fail label we're freeing pcap_t structure, so don't use p->errbuf,
but passed argument buffer.
Document nanosecond-resolution pcap files.
Revert "Document nanosecond-resolution pcap files."

This reverts commit 4a96c492ed05175d05b8cd311bfea0d978346067.